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Numerical Testing of Hypotheses for the Recent Thinning and Acceleration of Greenland Outlet Glaciers

Background

The aim of this research is to better understand the current rapid thinning and flow acceleration of outlet glaciers of the Greenland ice sheet and assess their future dynamical response to climate change. This will be addressed by further development of an existing time-dependent numerical flowline model and applying it to two rapidly changing Greenland outlet glaciers with excellent observational data - Helheim Glacier (East Greenland) and Jakobshavn Isbrae (West Greenland).

The specific objectives of the modelling are to:

determine the response of the flow to an initial front retreat and investigate the upstream propagation of the resulting thinning with time

to investigate the feedback mechanisms involved in the retreat of the calving front/grounding line and their implications on the future behaviour by including a freely evolving grounding line. The model results will be compared with data from remote sensing

Findings

Recent rapid dynamic changes of Greenland’s outlet glaciers raised concerns over the contribution to future sea level rise. These dynamic changes seem to be linked to the warming trend in Greenland, but the mechanisms that link climate and ice dynamics are poorly understood, and current numerical models of ice sheets are not able to simulate these changes realistically. These dynamic changes therefore provide major uncertainties in the predictions of mass loss from the Greenland ice sheet. We developed a numerical ice-flow model that reproduces the observed rapid changes in Helheim Glacier, one of Greenland’s largest outlet glaciers. Our simulations show that the ice acceleration, thinning and retreat begin at the calving terminus and then propagate upstream through dynamic

coupling along the glacier. We find that these changes are unlikely to be caused by basal lubrication through enhanced surface melt from the recent atmospheric warming. The modelling further shows that tidewater outlet glaciers adjust extremely rapidly to changing boundary conditions at the calving terminus and implies that the recent rates of mass loss in Greenland’s outlet glaciers are transient and should not be extrapolated into the future.